Interpretive Summary: Corn can be a healthy whole-grain food source to combat obesity, an epidemic in this country. Compared to other grains, corn has a lower glycemic index which can be even lower with higher levels of resistant starch (RS), the fraction of dietary starch fermented in the large intestine. By analyzing a set of 60 high-yielding breeding lines containing exotic germplasm for their starch thermal characteristics and level of RS, we were able to show that the location in which they were grown influenced the values of the starch characteristic. Even though the starch values were within normal limits, there were significant differences among the lines. Some thermal characteristics were correlated with the level of RS. All of these findings indicate that we would be able to successfully select for higher RS values in high-yielding corn lines. High-yielding hybrds with high levels of RS would open new opportunities for farmers and food companies to supply consumers with healthy corn food products to combat obesity.

Technical Abstract:
Corn as a food that is heated and cooled to allow starch retrogradation has higher levels of resistant starch (RS). Increasing the amount of RS can make corn an even healthier food and may be accomplished by breeding and selection, especially by using exotic germplasm. Sixty breeding lines of introgressed exotic germplasm backgrounds, selected for high yield, were grown in three tropical and temperate locations and analyzed for starch thermal characteristics and RS levels. Although actual values for all starch characteristics were within normal levels, most characteristics had significant genotypic effects, and all had significant location effects. A significant genotype effect for RS levels indicates that genotypic selection to raise the level of RS and increasing the healthful aspects of corn food should be successful. Significant location effects indicates that breeders using winter nurseries to accelerate their breeding progress need to be careful when making selections using RS data collected on seed grown in the tropics. A small but highly significant correlation between RS and some thermal characteristics, especially percentage of retrogradation, indicates that we may be able to select promising genotypes for RS selection based on our extensive database of thermal characteristics collected on a wide number of diverse corn lines.